Water levels at China's giant Three Gorges Dam on the Yangtze river are inching closer to their maximum after torrential rains raised inflows to a record high, official data showed Friday.

With 75,000 cubic meters per second of water flowing in from the Yangtze river on Thursday, the reservoir's depths reached 165.6 meters by Friday morning, up more than 2 meters overnight and almost 20 meters higher than the official warning level.

The maximum designed depth of China's largest reservoir is 175 meters.

Authorities raised the discharge volume to a record 48,800 cubic meters per second Thursday to try to lower water levels, and they might have to increase it again to avoid the possibility of a dangerous overflow.

"They will do everything they can to prevent the dam from overtopping," said Desiree Tullos, a professor at Oregon State University who studies the Three Gorges project.

"An overtopping dam is a worst-case scenario because it produces significant damage ... and can lead to the entire thing collapsing."

Rainfall in the Yangtze basin has been well over double the seasonal average this year. The floods had caused nearly 180 billion yuan ($26 billion) in economic damages by last week, and 63 million people have been affected.

The Three Gorges Project, completed in 2012, was designed not only to generate power but also to tame the fierce Yangtze, the cause of many devastating floods throughout China's history.

China's giant hydroelectric dams have stored more than 100 billion cubic meters of floodwater this year, and shielded 18.5 million residents from evacuation, according to government figures. The Three Gorges project alone has cut downstream floodwaters by 34%, officials said.

But opponents say the flood control capability of the Three Gorges Dam is limited, and it could even make the problem worse in the long term.